Barricaded within their station, the police admitted they could not repel the attacks and were terrified. "Of course we are," one told the Associated Press. "It's a natural reaction after what [has] happened in other parts of the country."

Meanwhile, supporters of Mr Aristide vowed to fight on. "We have machetes and guns and we will resist," said Pierre Frandley, a carpenter.

Aid agencies called for urgent international action, claiming that Haiti was "on the verge of a generalised civil war", as radio stations said that police officers in four towns had deserted their posts.

Mr Aristide rebuffed US suggestions that he convene early presidential elections as a way to defuse the crisis, a senior US official said last night.

Radio Metropole, a station sympathetic to opponents of Mr Aristide, reported that police had abandoned their posts in the central towns of Mireblais, Savanette and Las Cahobas, as well as Belladere on the western border with the Dominican Republic, the latest sign that the small, demoralised force is no match for rebels joined this week by former soldiers of Haiti's disbanded army.

The political crisis has accelerated rapidly in the past two weeks as political opposition to Mr Aristide in the capital, Port-au-Prince, has been bolstered in the provinces by armed gangs. Their forces were strengthened at the weekend by the return of death squad leaders and ex-soldiers from the former dictatorship.

"The army is no longer demobilised. The army is mobilised," said Jean-Baptiste Joseph, a former sergeant who was jailed in the 1990s for plotting insurrection.

Amnesty International said yesterday: "As rebel forces under the leadership of convicted human rights abusers expand their control in the centre and north of the country, and the population of conflict areas is cut off from supplies of food and medicines, fears of a mass refugee outflow are bound to increase."

Mr Aristide's critics are calling on him to resign, claiming he has lost credibility after rigging parliamentary elections in 2000 and presiding over human rights abuses.

He insists he will see out his term until 2006, and accuses his opponents of trying to oust him by unconstitutional means. But with no army and only 4,000 policemen, he has become increasingly reliant on gangs loyal to his Lavalas party. Efforts at mediation by the Organisation of American States and the Caribbean community, Caricom, have failed.

France, Haiti's former colonising power which has 4,000 troops in its Caribbean territories, is considering sending a peacekeeping force, or proposing the UN do so. However, the French government would first like to see some prospect of reconciliation between both sides.

"An intervention force _ implies a stop to the violence, a restart to dialogue," said the French foreign minister, Dominique de Villepin. "Nothing will be possible in Haiti if there isn't a jolt."

The US and the European Union are pressing both sides to reach a political solution. "The EU strongly believes that the present crisis in Haiti must be resolved peacefully by seeking dialogue and compromise," an EU statement said yesterday. "All constitutional solutions should be considered."

The UN secretary general, Kofi Annan, said the world body was planning to become "much more actively engaged" in Haiti's crisis.

In the fourth largest city, Gonaives, food reached the town for the first time since the rebels took control two weeks ago. As lorries arrived with lentils and millet, rebels fired shots in the air to prevent residents from stampeding them. One woman was hospitalised after being trampled.